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FieldListDiskBlockReader.hpp

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/*==========================================================================
 * Copyright (c) 2004 University of Massachusetts.  All Rights Reserved.
 *
 * Use of the Lemur Toolkit for Language Modeling and Information Retrieval
 * is subject to the terms of the software license set forth in the LICENSE
 * file included with this software, and also available at
 * http://www.lemurproject.org/license.html
 *
 *==========================================================================
*/


//
// FieldListDiskBlockReader.hpp
//
// 10 February 2004 -- tds
//

#ifndef INDRI_KEYFILEFIELDLISTDISKBLOCKREADER_HPP
#define INDRI_KEYFILEFIELDLISTDISKBLOCKREADER_HPP

#include "indri/Extent.hpp"
#include "indri/FieldListDiskBlockWriter.hpp"

class FieldListDiskBlockReader {
private:
  Extent _extent;
  const char* _current;
  const char* _block;
  int _extentCount;
  int _document;
  int _endByte;
  bool _numeric;
  INT64 _number;

public:
  void setBlock( const char* block ) {
    _block = block;
    _current = block;
    _document = 0;
    _extentCount = 0;
    _extent.begin = 0;
    _extent.end = 0;
    _number = 0;

    int endAndNumeric = * (int*) ( _block + INDRI_FIELDLIST_BLOCKSIZE - 2*sizeof(int) );
    _numeric = (endAndNumeric & 0x80000000) ? true : false;
    _endByte = endAndNumeric & 0x7fffffff;
  }

  int lastDocument() {
    return * (int*) ( _block + INDRI_FIELDLIST_BLOCKSIZE - sizeof(int) );
  }

  bool next() {
    if( ! _extentCount ) {
      if( !hasMore() )
        return false;

      int documentDelta;

      _current = RVLCompress::decompress_int( _current, documentDelta );
      _current = RVLCompress::decompress_int( _current, _extentCount );
      _document += documentDelta;
    
      _extent.begin = 0;
      _extent.end = 0;
    }

    int beginDelta;
    int endDelta;

    _current = RVLCompress::decompress_int( _current, beginDelta );
    _current = RVLCompress::decompress_int( _current, endDelta );

    if( _numeric ) {
      _current = RVLCompress::decompress_longlong( _current, _number );
    }

    assert( _current < _block + INDRI_FIELDLIST_BLOCKSIZE );

    _extentCount--;
    _extent.begin = _extent.end + beginDelta;
    _extent.end = _extent.begin + endDelta;
    return true;
  }

  int document() const {
    return _document;
  }

  INT64 number() const {
    return _number;
  }

  const Extent& extent() const {
    return _extent;
  }

  bool hasMore() {
    return _endByte > _current - _block;
  }
};

#endif // INDRI_FIELDLISTDISKBLOCKREADER_HPP

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